Recombinant DNA technology has many potential uses. One use which is presently emerging is to utilize the protein products to prepare vaccines. This procedure involves the insertion of a DNA sequence coding for an antigenic substance into a transfer vector, transforming microorganism with this transfer vector and expressing the DNA sequence either directly or as a fusion protein. The protein product produced by the microorganism is antigenic and is capable of eliciting antibodies which are cross-reactive with the native antigen. Thus, the protein product can be administered as a vaccine to provide immunological protection against the native antigen. This aspect of recombinant DNA technology is particularly important in those cases where it is difficult to isolate enough antigenic material to prepare sufficient quantities of antibodies. Transformed microorganisms will be able to produce large quantities of antigenic material so that it will be practical to prepare vaccines for many additional diseases. An example of this particular technology is described in European Patent Application No. 0013828. This application describes the cloning of the Hepatitis B virus and demonstrates the ability of the expression products to elicit formation of antibodies in rabbits. Thus, it is possible to use the expression products of the cloned virus in a vaccine. Similarly, S. Cohen, in a letter to Nature (288, 8 (1980)), indicated that significant progress had been made in cloning the antigenic materials of malaria and that production of malaria vaccines was not far behind.
It has been recognized that many diseases, including viral infections, are characterized by the presence of more than one antigenic species. For example, the Hepatitis B virus has at least two antigenic materials--the core antigen and the surface antigen. Similarly, many pathogenic E. coli have two enterotoxins--one is heat labile and the other is heat stabile. Although the latter is not antigenic in itself, it is capable of acting as a hapten. It is well known that one antigen will only elicit antibodies that recognize that particular antigen. Consequently, vaccines containing one antigen will only produce antibodies towards that antigen. A vaccine having two or more antigens or a combination of two or more vaccines will produce a corresponding number of antibodies, but each antibody will be specific for only one antigen.
It is an object of the present invention to overcome this deficiency of prior art vaccines. The present invention provides for the preparation of a vaccine containing a fusion protein comprising two or more different antigenic materials. The fusion protein is expressed by microorganisms from a deoxynucleotide sequence which comprises two or more sequences, each coding for a different antigenic material, linked together in phase. The fusion protein elicits the formation of an antibody which is multivalent, i.e., the antibody is specific for each antigenic material. Consequently, the antibody can cross-react with any or all of the native antigenic materials and thus provide better protection, since the vaccine is directed to several antigenic materials. As used herein, antigenic material may refer to a substance which is antigenic per se or a substance which can act as a hapten. In addition, antigenic material as used herein refers to antigenic material exogenous to the host transfer vector or expression vector into which the antigenic material is inserted.